THE THERMO-ELECTRIC EFFECT

By, Prajwal Keranahalli

WHAT IS IT?

The thermoelectric effect is the direct conversion of temperature differences to electric voltage or vice-versa.

The direction of heat flow can be controlled by changing polarity of the voltage source

HISTORY

In the 1820’s Thomas Seebeck (Germany) discovered that if two metals at different temperatures were touching you could create an electric current

Jean Peltier discovered that the opposite was also true. By sending a current through two metals you could create differences in temperature

WHY DOES THIS EFFECT OCCUR?

Charge Carrier Diffusion and Phonon Drag

Seebeck Effect

Peltier Effect

THERMOELECTRIC MODULE

THE ZEROTH LAW OF THERMODYNAMICS

Pairs of P and N type conductors are both it contact with a copper plate.

There will thermo power until the system is at equilibrium. (All three materials are at the same temperature)

SEMICONDUCTORS

Semiconductors have an electrical conductivity between materials like copper and glass

They possess and interesting property where its conductivity increases with added temperature

P and N type (thermocouples) semiconductors are created by doping.

PHYSICS BEHIND IT

Efficiency= e =

Voltage = V = (SB-SA)*(T2-T1)

Thermo Power (V/K) = S = -

THERMAL CONDUCTIVITY OF CERAMICS

Pcond = kA((Th-Tc)/L) k=1.5

A= 0.03 m2

Th=100C

Tc=RT (21C)

L=0.005m

711 W/m/°C

APPLICATIONS Thermoelectric generator Cooling Computers Drink Coolers Recharging Devices Space Probes Solar Power Clothing Useful, Quiet, no Moving Parts It is less efficient (10%) and more expensive

TEST FOR UNDERSTANDING

The USB Coffee cup warmer is an example of the Seebeck Effect or the Peltier Effect?

Before the P and N type Semiconductors what material were used instead as thermal couples for thermoelectric modules?

What are the advantages of using thermoelectric generators over, for example heat engines?

REFERENCES

Rockwood, Alan L. (1984). "Relationship of thermoelectricity to electronic entropy". Phys. Rev. A 30 (5): 2843–4. Bibcode 1984PhRvA..30.2843R. doi:10.1103/PhysRevA.30.2843

G. Jeffrey Snyder and Eric S. Toberer "Complex Thermoelectric Materials" Nature Materials 7, 105-114 (2008).

CRC Handbook of Thermoelectrics, Introduction, Edited by D.M. Rowe, CRC Press, 1995.

G. Jeffrey Snyder, Tristan Ursell. "Thermoelectric efficiency and compatibility" Physical Review Letters, Vol 91 p. 148301 (2003)